SE455558B - TRANSISTORIZED RECTIFIER BRIDGE CIRCUIT WITH SHOCK STRIP PROTECTION - Google Patents

Description

connected to the anodes of a first and a second zener diode Z3 455 558 2.

The base of the transistor T1 is connected to the b-conductor of the line via a resistor R1, and the base of the transistor T3 is connected to this conductor via a resistor H3. The base of the transistor T2 is connected to the a-conductor of the line via a resistor H2, and the base of the transistor Tu is connected to the same conductor via a resistor Ru. These resistors are dimensioned for suitable bias voltage of the bridge transistors, which are grounded under normal operating conditions. K1ämman _ "-" är an- resp.

Zu, whose cathodes are connected to the a-conductor and b-conductor of the line, respectively. At a given polarity of the line, only the PNP transistor, whose emitter is connected to the higher potential line terminal, and the NPN transistor, whose emitter is connected to the lower potential line terminal, conduct. The other two transistors are choked. Consequently, regardless of the actual polarity of the line, the supply current will always flow through the telephone circuit C 'from the terminal formed by the connection between the collectors of the PNP transistors to the terminal formed by the connection between the collectors of the NPN transistors. The polarity at these clamps is constant.

A possible current surge in the line causes the total voltage drop in the rectifier circuit to increase.

However, as soon as the terminal voltage across the zener diode, the cathode of which is connected to the conductor with the highest potential, becomes equal to the breakdown voltage VZ of the diode junction, this diode begins to conduct the reverse direction due to the zener power. The second zener diode, on the other hand, begins to conduct like a normal diode as soon as its terminal voltage becomes equal to the threshold voltage VONZ for conduction in the forward direction.

Consequently, the total voltage drop of the rectifier circuit will not exceed the maximum value VR MAX = Vz "VoNz when surge currents occur on the line.

The maximum voltage applied to the electronic circuit of the telephone does not exceed the maximum value V = V - V CMAX Z CE Sat where V is equal to the collector-emitter CE set voltage at the bottom of a PNP transistor in the bridge.

For this reason, both the rectifier circuit and the telephone circuit are protected against surge currents. <1 ..... .._ .Ef-f. . a _. v »fl- w- 55 UO 455 558 3 rectifier circuit equipped with surge protection is not the best solution with respect to However, one of the types described above is the manufacturing economy.

The addition of elements, such as the two bridge components of the power-enhancing circuit zener diodes, significantly increases the cost of the circuit (whether the circuit is composed of discrete components or is monolithically integrated) due to the fact known to those skilled in the art that this requires both integration area as additional process methods.

The present invention has for its object to provide a transistorised, shock-protected rectifier bridge circuit which can be monolithically integrated and which is useful for connecting the electronic circuits of a subscriber telephone set to a two-wire telephone line with low supply voltage, this rectifier bridge point being misk than previously known rectifier circuits with surge protection.

The above-mentioned object is achieved according to the invention in that the transistorized rectifier bridge circuit has the features defined in claim 1.

The invention is described in more detail below in the form of some exemplary but non-limiting exemplary embodiments shown in the accompanying drawing. Fig. 1 shows a schematic diagram of a transistorized rectifier bridge already described above with surge protection. Fig. 2 shows a schematic diagram of a transistorised rectifier bridge circuit according to the invention with surge protection. Fig. 3 shows a schematic diagram of another embodiment of the invention. In the figures, the same reference numerals are used to indicate against corresponding components.

The rectifier circuit shown in Fig. E and according to the invention comprises a bridge circuit device consisting of a pair of bipolar PNP transistors T1, T2 and a pair of bipolar NPN transistors TB, Tu.

The collector of the transistor T1 is connected to the collector of the transistor T2, and the collector of the transistor T3 is connected to the collector of the transistor T1. These two connections form a first terminal, denoted by "+" and a second, denoted by "-", to which are connected the electronic circuit C of the telephone set to be connected to the line.

The emitters of the transistors T1 and T3 are connected to a first conductor a in the two-wire telephone line. The transmitters T2 and 50 455 558 1, T emitters are connected to the second conductor b of the line.

The base of the transistor T1 is connected to the b-conductor via a resistor R1, and the base of the transistor T3 is connected to this conductor 3. The base of the transistor T2 is connected to the a-conductor via a resistor H2, and the base of the transistor Tu is connected via a resistor resistor R to this conductor via a resistor Ru. The base of the transistor T3 is also connected to the emitter of a bipolar NPN transistor Tlš, the base and collector of which are connected to the collector of the transistor T3.

The base of the transistor Tu is also connected to the emitter of a bipolar NPN transistor Tlu, the base and collector of which are connected to the collector of the transistor Tu.

Fig. 3 shows the schematic diagram of another embodiment of the invention comprising a pair of bipolar PNP transistors T1, T2 and two pairs of bipolar NPN transistors T3, TS and Tu, T6.

The collector of the transistor T1 is connected to the collector of the transistor T2, and the collector of the transistor T5 is connected to the collector of the transistor T6. These two connections form a first terminal denoted by "+" and a second terminal denoted by "-", to which the electronic circuit C of the telephone set to be connected to the line is connected.

The emitter of the transistor TS is connected to the collector of the transistor T3 and the emitter of the transistor T6 to the collector of the transistor Tu.

The emitters of the transistors T1 and T3 are connected to a first conductor a in the two-wire telephone line. The emitters of the transistors T2 and Tu are connected to the other conductors b of the line b.

The figure does not show the biasing means well known to those skilled in the art, to which the base electrodes of the transistors T1, T2, T3, Tu, T and T6 are connected. The circuit shown in Fig. 3 also contains two pairs of bipolar NPN transistors TIB, T15 and Tlu, TI6.

The emitters of the transistors Tlš and TIS are connected to the emitters of the transistor T3 and are connected to the base and collector of the transistor Tu.

Base and collector of both the transistor TI; are connected to the T5 collector of the transistor. Base and collector at base and collector respectively. The transistors Tlu and T16 of the transistors T1 and T16 as the transistors T11 and T11 are connected to the collector of the transistor T6.

The function of the circuit shown in Fig. 2 is as follows.

Under normal operating conditions, the transistors T1, Tu V-.¿h - + I ~ "~ '~ - 455 558 or the transistors T2, Tu are conducting in accordance with the conduction polarity. The conducting transistors are bottomed. The transistors biased in the reverse direction T13 and Tlu are strangled.

A possible surge current on the line causes an increase in the total voltage drop in the rectifier circuit. Assuming that the voltage at the line terminals has such a polarity that it transitions under normal conditions, the transistor T5 will start the gates T1 and Tu are bottomed and the transistors T2 and T restrict lead in the reverse direction as soon as its emitter-collector voltage - due to the surge current - becomes equal to the breakdown voltage BV between emitter and collector at open base. The transistor T, ECO T3 13, which is biased in the reverse direction of the base-collector voltage of the transistor T3, remains throttled.

After the breakthrough, the transistor T3 can be passed by very high currents without increasing its collector-emitter voltage, so that the terminal voltage of the electronic telephone circuit connected to the bridge does not exceed the maximum value vc MAX = Bvaco TB 'VCE san Tl where VCE Sat T1 is the collector of the transistor T1. emitter voltage at bottom.

The total current from the transistors T1 and T3 passes through the collector of the transistor Tu, and since this transistor has an unchanged base bias state, it will no longer bottom out but will start working in its active range.

In the active area, the collector-emitter voltage of the transistor Tu increases with increasing collector current. When this voltage becomes equal to the sum of the base-emitter voltage VBE Tu of the transistor Tu and the threshold line voltage VBB T at the base-emitter junction of the diode-shorted transistor Tlu, this transistor Tlu begins to supply current to the base of the transistor Tu, which can increase its lead without further. increases in the collector-emitter voltage.

The total voltage drop across the rectifier bridge therefore does not exceed the maximum value. I V V R MAX Bvaco TB * Vas Tu + BE Tlu.

Thus, both the rectifier circuit and the telephone circuit are protected against surge currents on the line using the bridge transistors as protective elements.

BO Ä0 455 558 The circuit operates in an identical and symmetrical manner when the line voltage is of opposite polarity. The value of the voltage BVECO for the transistors Tj and Tu is regulated in an appropriate manner by using known base doping methods.

However, when the normal line voltage is already high, and therefore the BVECO voltage for the bridge NPN transistors must be high, so that the throttled NPN transistor under normal operating conditions does not become conductive due to breakthrough in the reverse direction, it is advisable to use two pair of NPN transistors in cascade, as illustrated in Fig. 3. In this case, a variant of the circuit for protection against surge currents is also shown. The circuit means used for biasing the transistors of the bridge, which are not shown but are easily realized by the person skilled in the art, are necessarily more complicated than in Figs. 1 and 2.

In the normal operating condition of the circuit shown in Fig. 3, depending on the line polarity fl, either only the transistors T1, Tu and T6 or the transistors T2, T3 and T5 conduct.

The conducting transistors are grounded at the given bias states.

Assuming that the conductor a of the telephone line has a higher potential than the conductor b, the transistors T1, Tu and T6 will be grounded.

The diode-connected transistors T1 ”and TI6 do not conduct, since their collector-emitter voltages are too low as a result of the grounded states of transistors Tu and T6.

A possible surge current on the line causes an increase in the total voltage drop of the rectifier circuit. As soon as the emitter-collector voltage of the transistors T5 and TS becomes equal to that of these transistors) from emitter to carbon breakdown voltage (BVECO T or BV ECO T5 lecturer at open base, transistors T3 and T5 start to conduct in the reverse direction. For example, the terminal voltage of the electronic telephone circuit will not exceed the maximum value vc MAX = Bvx-: co m3 "BVEco TS 'VCE san' rl where VCE Sat Tl is the collector-emitter voltage of the transistor T1 at bottom.

The total current from the transistors T1, T3 and T5 flows to the collector of the transistor T6, so that this transistor, due to the fact that its base bias state is unchanged, changes from bottoming to the active zone of its operating range.

BO 455 558 Within the active zone, the collector-emitter voltage of the transistor T6 increases with increasing collector current, until conduction is enabled by the transistor TIS.

The emitter current of the transistors T6 and T16 flows to the collector of the transistor T1, so that this transistor, like the transistor T6, begins to operate in its active zone, whereby its collector-base voltage increases with the collector current until the transistor Tlu can start conducting. To absorb the total current from the transistors T16 and T6, now - independent of the transistor T6 - the current can increase through the transistor Tu, which receives the required base current from the transistor Tlu. This current increase occurs without further increase of the transistor Tu collector-emitter voltage.

The total voltage drop across the rectifier bridge does not exceed the maximum value 4 '4' + BV 3 ECO T5 constitutes the base of the transistor Tu and Tlu respectively VR MAX Bvaco T VBB Tu VBB Tlu where V and V BE Tu BE Tlu emitter voltage at conduction state.

When the line voltage has the opposite polarity, the circuit operates in an identical and symmetrical manner. The embodiment of the invention shown in Fig. 3 also makes it possible for both the rectifier circuit and the telephone circuit connected thereto to be protected against surge currents on the line using the bridge elements themselves as protective elements.

The rectifier circuit constructed in accordance with the invention is particularly well suited to be integrated in a monolithic semiconductor block using known integration methods.

Transistors Tlš, Tlu, T15 and T16 are conventional low cost NPN transistors. An integrated circuit designed in accordance with the invention is therefore advantageous both from a manufacturing point of view and with regard to the size of the integration areas.

The economic benefits are obvious even in an embodiment where discrete components are used. Although two embodiments of the invention have been described above, it is obvious that a number of variants are possible without departing from the scope of the invention. For example, in any construction, it is possible to use the bridge's PNP transistors instead of its NPN transistors as protection elements.

Claims (10)

455 558 K Patent claims 1. l. Transistorized rectifier bridge circuit with surge protection and intended for connecting the electronic circuit of a subscriber telephone to a two-wire telephone line, which bridge circuit comprises a first, a second, a third and a fourth bridge element (T1, T2, T3 and Tu), each having a first and a second terminal, the second terminal of the first element (T1) being connected to the second terminal of the second element (T2), while the second terminal of the third element (T3) are connected to the second terminal of the fourth element (Tu), which connections form a first and a second connection terminal (+ or -), to which the electronic circuit (C) of the telephone set is connected, and wherein the first and third elements ( T1, T3) first terminals are connected to a first conductor (a) in the telephone line, while the first terminals of the second and fourth elements (T2, Tu) are connected to the second conductor (b) of the line; each bridge element comprising at least one first bipolar transistor connected to its emitter and collector between the first and second terminals of the element in question, the emitter of the transistor being connected to the first terminal of the element; and the transistors of the first and second elements (T1, T2) are of opposite type to the transistors of the third and fourth elements (T3, Tu); and each of said transistors has its base connected to the polarity-responsive control circuit means (R1, R2, R3, Ru), which control the transistors of the first and fourth elements (T1, Tu) in opposite phase to the second and fourth transistors of the elements (T2, _T5), characterized in that the base of the first transistor of the third and fourth bridge elements (T3, Tu) is connected to the second terminal of the element in question by means of a first semiconductor element (Tlš, Tlu), which has a normal work permit reverse bipolar transition. 2. A bridge circuit according to claim 1, characterized in that said semiconductor element is a diode. 3. A bridge circuit as claimed in Claim 1, characterized in that said semiconductor element is a bipolar transistor (Tlš, Tlu), the base of which is short-circuited with the collector. H. A bridge circuit according to any one of the preceding claims, characterized in that each bridge element consists of a bipolar transistor, the emitter and collector of which constitute the first resp. second clamp. 455 558 Bridge circuit according to one of Claims 1 to 3, characterized in that the third and fourth bridge elements each comprise a second bipolar transistor (T5, T6), which is arranged with its emitter and collector between the two terminals of the clement. so that the emitter is connected to the collector of the first transistor (TB, Tu), which collector is also connected to the second terminal of the element in question via a second semiconductor element (T15, Tlö), which has a bipolar transition back biased in normal working conditions. A bridge circuit according to claim 5, characterized in that said second semiconductor element is a diode. Bridging circuit according to claim 5, characterized in that said second semiconductor element is a bipolar transistor (T15, Tló), the base of which is short-circuited by the collector. Bridge circuit according to one of the preceding claims, characterized in that the first and second bridge elements (T1, Ta) each consist of a bipolar transistor, the emitter and collector of which form the first and second terminals of the element in question, and that the third and fourth bridge elements each consist of a pair of cascaded bipolar transistors (T3, T5; Tu, T6), where the emitter of the first transistor and the collector of the second transistor in the pair constitute the first and second elements of the element in question. second clamp. Bridge circuit according to one of the preceding claims, characterized in that each bipolar transistor included in the first and second bridge elements is of the PNP type, while each bipolar transistor included in the third and fourth bridge elements is of the NPN type. type. 10. A bridge circuit according to any one of the preceding claims, characterized in that the whole circuit is integrated in a monolithic semiconductor block.